Electronic filters are used today to suppress noise, reject unwanted signals, or in some way manipulate the characteristics of an input signal. Typical semiconductor based filter designs comprise inductor, resistor and/or capacitor networks. Such networks are often placed together with separate transient voltage suppression (TVS) devices such as Zener diodes to provide ESD protection in addition to signal processing. The capacitance contribution of the TVS device often is used to further shape the filter characteristic.
One challenge semiconductor based filter designers face is providing an effective design in as small a space as possible in order to meet the size requirements that some applications demand. This challenge is often difficult, particularly when the filter design includes multiple channels and inductor structures. Specifically, the presence of inductor structures increases the likelihood of inter-channel coupling, which is an undesired effect.
Accordingly, a structure and method of manufacture are needed that, among other things, reduce inter-channel coupling effects in integrated filter designs.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. For clarity of the drawings, doped regions of device structures are illustrated as having generally straight line edges and precise angular corners. However, those skilled in the art understand that due to the diffusion and activation of dopants the edges of doped regions are generally not straight lines and the corners are not precise angles.
Moreover, although the present invention is described using an elliptic filter embodiment, it is understood that this is for illustrative purposes only, and that the present invention is suitable for other filter or resonant structures as well including but not limited to pi-RC filters, pi-LC filters, Chebyshev filters or Butterworth filters. Additionally, the present invention is suitable for those filters that include active components.